1. Field
Embodiments of the present invention relate to a pressure damping device for a brake system which minimizes pressure pulsations to increase brake fluid pressure supplied to a wheel cylinder in braking.
2. Description of the Related Art
Recently, various systems have been proposed to provide stronger and more stable braking force to a vehicle equipped with a brake system to perform braking. Examples of braking systems include an anti-lock brake system (ABS), which prevents slippage of a wheel when braking a vehicle, a brake traction control system (BTCS), which prevents slippage of drive wheels during sudden start or sudden acceleration, and an electronic stability control (ESC) system, which maintains a vehicle in a stable condition of driving by controlling brake fluid pressure with a combination of the ABS and the BTCS.
FIG. 1 is a view illustrating a conventional brake system. With reference to FIG. 1, the brake system includes a brake pedal 10 to receive operational force from a driver, a brake booster 11 to boost the effort on the brake pedal 10 using the pressure difference between vacuum pressure and atmospheric pressure made by the effort on the brake pedal 10, a master cylinder 20 to generate pressure through the brake booster 11, a first hydraulic circuit 40A to connect a first port 21 of the master cylinder 20 and two wheel cylinders 30 to control transfer of fluid pressure, and a second hydraulic circuit 40B to connect a second port 22 of the master cylinder 20 and the other two wheel cylinders 30 to control transfer of fluid pressure. The first hydraulic circuit 40A and the second hydraulic circuit 40B are arranged in a compact form in a hydraulic block 40.
Each of the first hydraulic circuit 40A and the second hydraulic circuit 40B includes solenoid valves 41 and 42 to control brake oil pressure transferred to two wheel brakes 30, a pump 44 to draw in oil from the wheel brakes 30 or the master cylinder 20 and pump the oil out, an low pressure accumulator 43 allowing the oil from the wheel brakes 30 to be temporarily stored therein, an orifice 46 to reduce pressure pulsations in fluid pressure pumped out by the pump 44, and an auxiliary oil path 48a to guide the oil from the master cylinder 20 such that the oil is drawn into the inlet of the pump 44.
The solenoid valves 41 and 42, which are connected with the upstream and downstream of the wheel brakes 30, are divided into Normally Open-type solenoid valves 41, which are disposed upstream of the respective wheel brakes 30 and kept open in normal times, and Normally Closed-type solenoid valves 42, which are disposed downstream of the respective wheel brakes 30 and kept closed in normal times. Opening and closing of the solenoid valves 41 and 42 are controlled by an electric control unit (ECU) (not shown), which senses the speed of the vehicle through wheel speed sensors disposed at the respective wheels, and according to braking with pressure reduction, the Normally Closed-type solenoid valves 42 are opened and oil from the wheel brakes 30 are temporarily stored in the low pressure accumulator 43.
The pump 44 is driven by a motor 45 to draw in the oil stored in the low pressure accumulator 43 and discharge the oil to the orifice 46 so as to transfer the fluid pressure to the wheel brakes 30 or the master cylinder 20.
Also, a main oil path 47a connecting the master cylinder 20 and the discharge outlet of the pump 44 to each other is provided with the orifice 46 and a Normally Open-type solenoid valve 47 for control of a TCS (hereinafter, referred to as a TC valve) is installed at the main oil path 47a. The TC valve 47 is kept open in normal times, such that, in normal braking through the brake pedal 10, the brake fluid pressure formed in the master cylinder 20 is transferred to the wheel cylinders 30 through the main oil path 47a. 
The auxiliary oil path 48a, which branches from the main oil path 47a to guide the oil from the master cylinder 20 to the inlet of the pump 44 through which the oil is drawn in, is provided with a shuttle valve 48 allowing the oil to flow only into the inlet of the pump 44 installed therein. The shuttle valve 48, which operates electrically, is installed in the middle of the auxiliary oil path 48a such that it is kept closed in normal times and opened in the TCS mode.
Reference numeral 49 represents a check valve installed at a proper position in the oil path, and reference numeral 50 represents a pressure sensor to sense brake pressure transferred to the TC valve 47 and the shuttle valve 48.
In the brake system as above, pressure pulsations are generated in the fluid pressure pumped by the pump 44 according to operation of the motor 45 in braking. If a special change occurs, the pressure pulsations are reduced. Reduction of the pressure pulsations reduces torque transmitted to the motor 45, and consequently increases the rotational speed of the motor 45, thereby enhancing the rate of increase in pressure. That is, increase in pressure may allow quick transfer of the fluid pressure to the wheel brakes 30 to ensure stable braking.
The conventional brake system has the orifice 46 in the main oil path 47a to reduce pressure pulsations generated in the fluid pressure discharged from the pump 44, but it may not ensure smooth attenuation of the pressure pulsations as only the orifice 46 is provided to reduce the pressure pulsations.